Sample holder for accelerated fade apparatus and method of its use

ABSTRACT

The invention relates to an apparatus for light fastness testing. The apparatus for holding samples for testing comprising a planar member and vacuum to hold a sample against the test area of the planar member. A heating and cooling device in contact with said planar member, a heat sink, in contact with the heating and cooling device and a fan to direct air over the heat sink.

FIELD OF THE INVENTION

This invention relates to apparatus for testing material for lightfastness and deterioration under light. It particularly relates to amachine and method for testing of photographic materials.

BACKGROUND OF THE INVENTION

The testing of photographic materials for stability to light is carriedout in order to predict the behaviors of such materials years in thefuture. Generally these tests are accelerated by applying relativelyhigh levels of exposure to the materials for periods of between 3 weeksand 6 months, sometimes under elevated temperature conditions. Thetesting devices generally provide about 50K lux light. The typicaldevice has a group of stationary light sources or a single 360° lightsource located inside a generally spherical arrangement. The samples areattached to the inside of the spherical framework, and the framework isrotated around the light source.

In another type of device, the light is in a box, and samples arearranged at various distances from the light source in order to obtainthe exposure over a time period. In the box arrangement, the humidityand temperature also may be controlled to provide further acceleratedaging effects or to simulate the use of the photograph in high exposureconditions.

Devices for testing light fastness also have been utilized in the paintand dye industry. Some such devices are merely arrangements of materialsin areas such as Florida where there is a high percentage of sunlightavailable.

The previous devices suffered from several disadvantages. The longexposure periods required of 3 weeks to 6 months required researchprojects involving a need to know of stability improvements to proceedvery slowly. Further, the light sources would vary in intensity over theterm of the test as bulbs were replaced or aged so the test device putsout a different amount and quality of light. In addition, it was oftendifficult to control humidity and temperature conditions during the6-month test, as the seasonal changes in the typical office orlaboratory building occurred.

U.S. Pat. No. 5,138,892--Suga discloses a test device with the centrallight source with samples rotating around the source. U.S. Pat. No.4,704,903--Suga et al discloses a light fastness testing machine withair flow control. U.S. Pat. No. 4,544,995--Suga discloses a lightfastness testing machine with humidity control. U.S. Pat. No.4,760,748--Katayanagi et al discloses a testing device with rotation ofsamples around a central light source.

PROBLEM TO BE SOLVED BY THE INVENTION

There is a need for a device to accurately, repeatably, and rapidlysubject photographic materials to accelerated light fastness testing andfor a device to hold samples for testing.

SUMMARY OF THE INVENTION

It is an object of the invention to overcome difficulties in colorstability testing of prior apparatus and methods.

It is another object of the invention to provide reliable lightstability data in about two days.

It is another object of the invention to provide repeatable lightstability data.

It is another object of the invention to provide a means to hold testsamples at controlled temperature and distance from a light source foraccelerated fade.

These and other objects of the invention generally are provided byproviding apparatus for holding samples for testing comprising a planarmember, vacuum means to hold a sample against the test area of saidmember, a heating and cooling device in contact with said planar member,a heat sink, and a fan.

In another embodiment the invention provides apparatus for lightfastness testing comprising a light source, means for dividing visiblelight from ultraviolet and infrared radiation, means to direct thevisible component of light into spherical cavity, and means to mounttest samples in apertures in said cavity wherein said means to mounttest samples comprises apparatus for holding samples for testingcomprising a planar member, vacuum means to hold a sample against thetest area of said member, a heating and cooling device in contact withsaid planar member, a heat sink, and a fan.

ADVANTAGEOUS EFFECT OF THE INVENTION

The sample holder of the invention allows tests of multiple photographicsamples simultaneously. The sample holder has the advantage that thesamples are held flat at a constant temperature and light exposure. Thesample holder of the invention provides the ability to maintain sampletemperature constant even though ambient conditions change. The sampleholder of the invention also can hold temperature of the sample constanteven though the light exposure changes.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a side view of a schematic of the apparatus of the invention.

FIG. 2 is a top view of the apparatus of the invention.

FIG. 3 is a side view on cross-sectional line 3--3 of FIG. 2 of theapparatus of the invention.

FIG. 4 is a cross-sectional view on line 4--4 of FIG. 1 of the apparatusof the invention.

FIG. 5 is a graph illustrating a comparison of high intensity fade databetween the apparatus of the invention providing 600K lux of light witha prior art apparatus providing 50K lux. The results correlate verywell.

FIG. 6 is a side view of a sample holder in accordance with theinvention.

FIG. 7 is a top view of the sample holder of FIG. 6.

FIG. 8 is a top view of the plate which holds the samples.

FIG. 9 is a cross-sectional view of the plate of FIG. 8 on line 9--9.

DETAILED DESCRIPTION OF THE INVENTION

The invention has numerous advantages over prior apparatus and process.The invention has the advantage that it allows exposure of severalsamples at the same time to uniform light and temperature conditions.The apparatus of the invention provides control of sample temperature.By controlling sample temperature, the effect of aging factors otherthan light is minimized or may be tested. By having individualtemperature control of each sample holder, the same light unit may beutilized for testing of fade at different temperatures utilizing thesame exposure apparatus. The sample holder of the invention may beeasily removed from the test device for insertion of other sampleholders or for devices to test the amount of light being applied to aunit. The invention allows the rapid testing of samples under veryuniform and repeatable conditions. Further, the invention allows veryhigh exposure to light and surprisingly has been found to allowprediction of stability as accurately as the 6-month test at 50K lux.The device further is compact and reliable. The device allows thesamples themselves to have their temperature controlled independentlyfrom the amount of light to which they are exposed. The device furtherallows uniform exposure of all samples being tested at the same time.Present devices have a variance between exposure of samples in themiddle of the collection as opposed to samples at the edges. Theapparatus of the invention further allows repeatable results withdifferent apparatus rather than having tests of stability onlycomparable between samples tested in the same apparatus. The inventionprovides the advantage that light stability testing of photographicmaterials may be carried out rapidly. The invention further provides amethod and apparatus of light testing that is repeatable. The method andapparatus of the invention further provide the advantage that thetesting has temperature stability, as well as completion of testing toallow prediction of many years of fade based on a test lasting less thanthree weeks. These and other advantages will be apparent from thediscussion below.

FIG. 1 is a schematic illustration of the apparatus, utilizing to sampleholder, of the invention 10 from a side view. The device is enclosed bycovers 12 over the light source 14 over the mirror and light splitterand 16 over the fade chamber itself. FIG. 2 is a top view of theapparatus 10. In FIGS. 1 and 2, holders 18, 22, 24, and 26 are forsamples to be tested. The preferred holder of the invention is shown inFIGS. 6-9.

In the cross-sectional view of FIG. 3 taken on line 3--3 of FIG. 2,there is schematically shown a light source 28. Source 28 provides abeam of light that passes through the beam collimating lens 32. Thisprovides a collimated source that is focused onto the cold mirror 34splitter that allows the passage of unwanted radiation such as infraredrays and UV radiation to heat sink 36. The light 38 reflected by coldmirror splitter 34 and then passes through a heat absorber 35 before itenters chamber 42 that has an angular interior wall 44 and is formedfrom material 46 that is generally a white reflective material. Theapparatus 10 is provided with fan 48 and 52 which both direct air out ofthe device to cool the lamp and the heat sink. Further, air is directeddownward into the chamber 42 in order to provide cooling air past thesamples held by sample holders 18 and 22. The opening 54 has beenbeveled so as to prevent shadow areas on the sample exposed in opening54. The beveled edge 58 of opening 56 better shows the cross section ofthe opening allowing uniform exposure onto the test sample. Apparatus 10includes a base 15 that supports the apparatus 10.

FIG. 4 is a cross-sectional view of the chamber on line 4--4 of FIG. 1looking downward towards the inlet opening 62 where light enters thechamber 44. The chamber is provided with a sensing device 64 that readsthe intensity of light being applied to the surface of the chamber 44.This allows the intensity of the lamp to be adjusted to maintain theuniform and exact exposure at all times on the samples.

In FIG. 6 is illustrated a preferred apparatus for holding samples 72.This device as shown in side view comprises a fan 74, heat sink 76,heating and cooling Peltier Effect cooling device 78, and platen member82. Platen 82 has attached thereto vacuum manifold 84 with vacuumconnector 86 for a connection to a vacuum device not shown. Platen 82further is provided with an area for pin hinge device 88 and magneticlatching devices 92. Electrical leads 94 and 96 supply power to heatingand cooling device 78 from a power source not shown. In FIG. 7, fan 74is illustrated. The fan blades 98 direct the air up and away or towardsfrom the platen 82. They draw air or force air through vanes 102 of theheat sink device 76. The devices that make up the heat sink are held incontact by having suitable fasting or clamping means not shown.

The platen 82 with its attached vacuum chamber 84 is in contact with theheating and cooling device 78 which is in turn in contact with the heatsink 76. The use of the heat sink 76 in combination with the heating andcooling device 78 allows more rapid change of the platen 82 temperature.The platen and vacuum manifold 84 generally are formed of a materialwhich rapidly transfers heat such as aluminum or stainless steel.

Illustrated in FIG. 8 is a top view of the platen member 82. FIG. 9 is across-sectional view of the platen taken on line 9--9 of FIG. 8. FIGS. 8and 9 will be described together with platen 82 as a series of ridges104, 106, and 108. These ridges separate samples which may slide undersample holder 112. Sample holder 112 has bar 114 which aids in holdingthe samples to the platen 82 when the vacuum is not turned on. When thevacuum is turned on, the perforations 116 cause the samples to be heldagainst the platen. The holes 116 communicate with a chamber 118 that isconnected to vacuum source inlet 86. The vacuum pulling the samplesagainst the platen also serves to effectively transfer the temperatureof the platen to the samples providing better temperature control. Theholding of the sample flat against the platen also means that lightexposure is even and consistent. The sample holder of the invention maybe fastened to the exposure chamber by any convenient means. The sampleholder shown is provided with a hole for a hinge pin 88 and magnets 92that serve to hold the sample holder in place on cover 16, as well asproviding means to easily swing it out of the way for testing of thelight in the chamber or to change or read the samples. A variety ofclamps and hinges are known to those of ordinary skill in the art asmeans for fastening the sample holders to the chamber in an accuraterepeatable manner. The experiments have been performed to determine theeffectiveness of the heat sink properties of the sample holder asillustrated. It has been found that the sample holder utilizing themechanisms as described is able to maintain a sample temperature on theemulsion side, exposed to the light of a color paper sample at about 30degrees lower than the air temperature in the chamber. Given the airflow in the chamber, this is indication of good heat transfer and theability to maintain temperature sample at a constant temperature. In theoperation of the apparatus as described generally, the temperature inthe chamber generally will be between about 70° F. and 100° F. (21° C.and 38° C.). The cooling sample holder of the invention allows a sampleto be held at a temperature of about 75° (24° C.) for long-term tests.This allows the lamps to operate at maximum light output while achievingan accelerated aging data that is reliable and repeatable in predictinglong-term aging of color samples.

While the sample holder has been described for use with the highintensity light exposure chamber, they also could be utilized forholding samples in other environments. For instance, the sample holderscould be used to expose samples to print atmospheres of reactive gasesor to hold cloth samples for fading tests for cloth or for plasticsamples. The chamber and sample holders would be suitable for use intesting siding and paint samples.

The lamp utilized in the testing device of the invention may be anysuitable lamp that provides a strong enough light source. A preferredlamp has been found to be an Xenon illuminator incorporating reflectorand having a wattage of at least 500 watts. Such a lamp results in alight intensity in the chamber of between 500 and 600K lux by providingthe Xenon source external to the sample chamber 44. There allows auniform of exposure to light and generating less heat as the heatgenerating portion of the beam is removed by the cold mirror and heatabsorber. The mirror which reflects test light up into the chamber whileallowing splitting of the IR and UV portions which generate heat isformed of any material that will pass these kinds of radiation whilereflecting light. A preferred material has been found to be a coldmirror. In addition a heat absorber is used to minimize IR.

The fans that provide cooling air or flow are selected such that theyare able to remove heat from the system while providing air flowthroughout the device including down through the chamber.

The chamber itself has a white interior such that light will bereflected numerous times within the chamber resulting in uniformexposure to the samples in the four windows. The material forming thechamber may be any desirable material; however, a white thermoplasticresin known as Spectrolon, a trademark of Lab Spheres Corp., has beenfound to be suitable, as it is chemically inert and stable. Further, itprovides a surface that is white. It is anticipated that other materialscould be utilized that are white or have been coated with a whitesurface. The annular interior surface of the chamber provides aspherical area of any desired size allowing uniform exposure at a highlevel. Generally it has been found that a size of between 5 and 15inches in diameter is suitable. A preferred diameter has been found tobe about 6 inches for the Xenon illuminator of about 500 watts.

The control system comprising the sensor 64 and regulating device, notshown, to control the lamp to provide uniform power and response to thesensor may consist of operational integrator circuit.

As pointed out, the ports of the sphere where the samples are placedhave been angled to remove any shadowing due to the sphere wall'sthickness. It has generally been found that a 40-degree angle adjacentthe port openings will remove any shadows.

The exit holes where the samples are placed generally are of the size ofabout 11/2" square. In this space, several samples may be placed ifdesired. The sample temperatures are influenced by constant bathing ofthe sample with high velocity air from the fan 48 of FIG. 3. The sampleholders also may be provided with thermostats which would allow controlof the temperature in response to the sensed temperature of the samples.

The effectiveness of the invention device and sample holder was comparedwith samples faded by conventional long-term 50K lux fade over athree-week period. It was considered that if the long-term fade resultsover three weeks compared with the rapid fade of the invention deviceexposed at 600,000 Lux of light for 2 days were the same, then long-termfade prediction also would be the same. The device of the inventionexposing at 600K lux was operated on the samples for 2 days. The priordevice operating at 50K lux over three weeks was compared. As shown inFIG. 5, there is a fit of the delta densities.

This test was performed in the following manner: Samples treated by theinvention device were compared with samples treated by a conventionallong-term fade unit. It was considered that if there was a strongcorrelation between fade results for the two units then results obtainedwith the invention device would be predictive of long-term fade tests.

The device of the invention exposing at 600K lux was operated on thesamples for 2 days, while the conventional fade unit operated at 50K luxfor 3 weeks.

FIG. 5 compares fade results produced by the two units for a number ofdifferent color paper test samples. For each sample, its optical densitywas measured before and after testing and the resulting delta densitiesare plotted in FIG. 5. As seen in the figure, there is a high degree ofcorrelation (0.097) between the delta densities produced by theconventional and invention device fade.

While the above discussion presumes that photographic samples are beingtested, the invention device also would find use in the testing of fadeon paint samples and fabric samples. Samples of plastics, such as usedin siding and curtains, also could be tested with the inventionapparatus. To simulate fade of samples intended for exterior use, the UVand IR light would not be removed in order to better mimic the sun'srays. Samples of clothing often worn inside and for interior paintscould utilize light substantially as utilized for photographs. Thedevice could also be used with low light for low term tests under verystable conditions. Generally, photographic fading is conducted underconditions of interior light. It is known that window glass filters outUV rays; therefore, interior fade test does not consider the UV exposurefade as pertinent. The device also could be utilized to determine thefade characteristics of materials such as those incorporated in glassesto photochromically change upon being worn in high intensity lightareas. These and other uses are apparent to those skilled in the art.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention.

We claim:
 1. Apparatus for light fastness testing comprising a lightsource, means for dividing visible light from ultraviolet and infraredradiation, means to direct the visible component of light into aspherical cavity, and means to mount test samples in apertures in saidcavity wherein said means to mount test samples comprises apparatus forholding the samples for testing comprising a planar member, vacuum meansto hold the samples against a test area of said member, a heating andcooling device in contact with said planar member, a heat sink incontact with said heating and cooling device, and a fan to pass air oversaid heat sink.
 2. The apparatus of claim 1 wherein said cavity iswhite.
 3. The apparatus of claim 1 wherein said cavity is between about5 and 15 inches in diameter.
 4. The apparatus of claim 1 furthercomprising air circulation means.
 5. The apparatus of claim 1 whereinsaid light source is at least of 500-watt power.
 6. The apparatus ofclaim 1 wherein test samples placed in said apertures have greater than500K lux of light applied to said test samples.
 7. The apparatus ofclaim 6 wherein between about 500,000 and 600,000 Lux are applied tosaid samples.
 8. The apparatus of claim 1 wherein said light source is acollimated light source.
 9. The apparatus of claim 1 further comprisinga heat sink for absorbing the ultraviolet and infrared radiation. 10.The apparatus of claim 1 wherein said means for dividing visible lightcomprises a cold mirror and a heat absorber.
 11. A method of testinglight fading of test samples comprising providing apparatus for lightfastness testing comprising a light source, means for dividing visiblelight from ultraviolet and infrared rays, means to direct the visiblecomponent of light into a spherical cavity, and means to mount the testsamples in apertures in said cavity, placing the test samples in saidapertures, and subjecting said samples to light levels of greater than500K lux, wherein said means to mount said test samples comprisesapparatus for holding said samples for testing comprising a planarmember, vacuum means to hold said samples against a test area of saidmember, a heating and cooling device in contact with said planar member,a heat sink in contact with said heating and cooling device, and a fanadjacent said heat sink.
 12. The method of claim 11 wherein 10 to 20days of light exposure are carried out which then allows for predictionof 20-year color paper fade.
 13. The method of claim 11 wherein saidlight source is at least of 500-watt power.
 14. The method of claim 11further comprising a heat sink for absorbing the infrared andultraviolet radiation.